The azo dyes have been used in various uses. The number of types of marketed azo dyes is about 3,000, and the intended uses thereof include many grounds, e.g., for clothes, printing, cosmetics, medical cares, and foods. Therefore, influences of the azo dyes on environments assumed to be, and considerable amounts of the azo dyes would spread to the natural world. Chung et al have reported that 50% or more of the azo dyes actually used remain in the natural world without changing or with gradually degrading (see, e.g., Chung et al., “Environ. Carcino. & Ecotox. Revs.” C18(1):51-74, 2000).
Recently, primarily in Europe, there has been a movement to regulate certain azo dyes with laws in the light of safety, and there is a tendency to establish an act concerning this. For example, in 1996, the use of textiles containing 20 types of aromatic amines produced by reductive decomposition of azo groups was regulated in Germany.
Therefore, the azo dyes with high safety have been required, and among others, development of dyes where compounds produced by reductive decomposition of the azo groups are stable and hardly decomposed has become important.